Power semiconductor devices, such as power MOSFETs, are widely used in electronic circuits. A function of a power device is to act as a switch that can be operated to regulate the supply of power. With the ever increasing demand for power supply to electronic devices such as, for example, portable computers, the ability of a power semiconductor device to handle larger current demands at a lower resistance is a highly sought after characteristic.
Referring to FIGS. 1A and 1B, a conventional power MOSFET includes, among other features, a plurality of parallel stripe trenches 20, which are formed in a base region 16. Each trench 20 supports a gate structure as is well known in the art.
Formed adjacent trenches 20 are source regions 26. In a typical device, source contact 28 makes electrical contact with source regions 26 and base region 16 in order to prevent parasitic devices from becoming operational.
In order to produce a device such as the one illustrated by FIGS. 1A and 1B, trenches 20 must be spaced far enough to allow source contact 28 to make good electrical contact with source regions 26 and base region 16. As a result, the density of trenches 20 (number of trenches per unit area), and thus the density of the active cells (density of the active cell being the number active cells occupied per unit area) in the device is limited by the space between trenches 20.
The limit on the density of active cells limits the power handling capability of the device. Specifically, increasing the cell density leads to a higher power capability typically with lower ON resistance (resistance of the device while operating), while lowering the cell density results in the opposite.
It would be desirable to have a structure and a method for increasing the cell density in a power semiconductor device in order to increase its power handling capability.